A New Family of Two‐Dimensional Zeolites Prepared from the Intermediate Layered Precursor IPC‐3P Obtained during the Synthesis of TUN Zeolite

Abstract

Abstract:The crystallization of zeolite TUN with 1,4-bis(N-methylpyrrolidinium)butane as template proceeds via an intermediate, designated IPC-3P, following the Ostwald rule of successsive transformations. This apparently layered transient product has been thoroughly investigated and found to consist of MWW monolayers stacked without alignment in register, i.e. disordered compared with MCM-22P. The structure was confirmed based on X-ray diffraction and HRTEM analysis. Layered zeolite precursor IPC-3P can be swollen and pillared affording combined micro-and mesoporous material with enhanced BET surface area (685 m 2 /g) and greater accessibility of Brønsted acid sites for bulky molecules. The latter was probed with 2,6-di-tert-butylpyridine (DTBP). IPC-3P and its modification create a new layered zeolite sub-family belonging to the MWW family. FTIR data indicate that (Al)MWW materials: MCM-22 and IPC-3 with Si/Al >20 exhibit lower relative ratio of Brønsted to Lewis acid sites than MCM-22 with Si/Al around 13, namely less than 2 vs. >3, respectively. This is maintained even upon pillaring and warrants further exploration of materials like IPC-3P with higher Al content. The unique XRD features of IPC-3P indicating mis-aligned stacking of layers and distinct from MCM-22P, are also seen in other MWW materials like EMM-10P, HM-MCM-22 (hexamethonium templated MCM-22), ITQ-30 and UZM-8 suggesting need for more detailed study of their identity and properties.

Two-Dimensional Zeolite Materials: Structural and Acidity Properties

“…The acid site strength of 2D and 3D MWW zeolites is also characterized by profiles of TPD-NH 3 , and similar conclusions to those from FTIR of adsorbed pyridine have been drawn. For MCM-36 or ITQ-2 that are prepared under harsh (high pH and high temperature) conditions, three peaks are often observed in the profiles that consist of a maximum peak at~608 K, a shoulder at 498 K, and a characteristic shoulder in the range of 720-850 K. These peaks are sequentially assigned to the physiosorbed NH 3 The accessibility of acid sites to large molecules has been probed by FTIR of adsorbed bulky organic molecules such as DTBP [28,62,156,187,235,238,258,264,269], dimethylquinoline (DMQ) [226,262], 2,2,4-trimethylpentane [26], and pivalonitrile [182]. Along with the total number of acid sites that are determined from pyridine adsorption, the fraction of acid sites accessible to the bulky molecules have also been assessed, as shown in Table 13.…”

From 3D to 2D zeolite catalytic materials

“…191 The swollen material exhibits a highly increased interlamellar distance (e.g. MWW: d-spacing 5.2 nm vs. 2.6 nm in MWW(P) 243 ). It should be noted that the materials prepared using a surfactant 203 are swollen intrinsically but in contrast the surfactant tail is not easily removed from interlayer space as it is part of the SDA.…”

Mechanochemically assisted hydrolysis in the ADOR process

“…Direct connection of the layers via bridging oxygen atoms leads to IPC-4 (assigned the zeolite framework code PCR). 17 It is also possible to reintroduce silicon between the layers as square s4r units, either under highly acidic hydrolysis conditions (e.g. 12 M hydrochloric acid, HCl) or through the addition of a secondary silicon precursor such as diethoxydimethylsilane, resulting in IPC-2 (OKO).…”